Foil decoration is utilized so as to be effected on the surface of the molded body at the same time as injection molding of the resin molded body, thereby producing, for example, the molded article 13 as shown in FIG. 44, on the surface of which a pattern 11 and letters 12 are formed. A molding apparatus 10 as shown in FIG. 45 is used for the injection-molded-in foil decoration. (See the bulletins of Japanese Laid-open Patent Application No. 59-31130 and Japanese Patent Publication No. 4-42172.)
This apparatus 10 is provided with a female die 20 and a male die 25 arranged to be opposed to the female die 20. The female die 20 has a molding cavity 21 corresponding to the contour of the molded body to be obtained and suction ports 22 passing through the inside to open to the cavity 21, and is arranged to be translated in approaching-leaving directions relative to the male die 25 by a translating unit 23 composed of a cylinder, etc. Further, the male die 25 has a core 26, which is to be inserted into the cavity 21, and a pouring port (gate) 27 of a molten-resin-injecting unit is formed therein. Further, a hot platen 29 is arranged as movable into or away from between the female die 20 and the male die 25. This hot platen 29 includes its front surface (on the female die 20 side) as a heating surface.
In order to effect foil decoration at the same time as injection molding using such an apparatus 10, a decoration sheet 15 is first set to be opposed to the molding cavity of female die 20, and the decoration sheet 15 is heated to soften by the hot platen 29 (FIG. 45). Then the decoration sheet 15 is pinched between the female die 20 and the hot platen 29 so as to close an opening face of the cavity 21, the cavity is evacuated through the suction ports 22 formed in the female die 20, and compressed air is supplied through an air vent (not shown) provided in the hot platen 29 as occasion demands.
It makes the decoration sheet 15 stretched along the inner periphery of cavity 21 as adhering thereto in fit, as shown in FIG. 46. Here, this step is generally called as premolding.
Next, after the hot platen 29 is withdrawn from between the both dies, as shown in FIG. 47, the female die 20 is advanced to be coupled with the male die 25, thereby effecting clamping of the dies. Thereafter, into a cavity space formed between the female die 20 and the male die 25, a molten resin is poured and charged through the pouring port 27 of the injecting unit provided in the male die 25, thereby effecting injection molding.
Thus, the decoration sheet 15 in the female die 25 becomes integrated with the resin injected (molded body P) to adhere thereto. When the dies are opened after completion of injection molding, the molded body can be taken out of the dies as the decoration sheet is adhered to the outer surface.
Here, if the decoration sheet 15 is a bonded and layered film (laminate film), the foil decoration is completed at that stage, and all layers of the decoration sheet 15 are adhered to integrate onto the outer surface of the molded body P to form a decorative layer. On the other hand, if the decoration sheet 15 is a transfer film, only a base film of the decoration sheet 15 integrated onto the outer surface of the molded body P is released in a later step, so that a transfer layer such as a pattern layer is left on the molded body P side to form a decorative layer, thereby completing the foil decoration.
Since in the conventional processes for effecting injection-molded-in foil decoration the decoration sheet is set on the opening surface side of the molding cavity in the female die and then is pushed into the molding cavity by evacuation or by the core member, whereby the sheet is drawn toward the cavity inner periphery (cavity surface) at a stretch in a short period of time to become laid along it, the decoration sheet has to be stretched at high speed in the mold cavity. Stretching amounts of the decoration sheet in the dies become larger as the level difference or curvature of the surface of molded body becomes greater. Further, if the sheet is stretched at high speed, distribution of stresses cannot be sufficiently dispersed or relaxed, which causes the stretching amounts to be concentrated locally. When the decoration sheet is locally stretched to a large extent, the pattern layer or the like formed thereon is naturally stretched as well, which could result in distorting the pattern layer to an unignorable extent or which could cause positional deviation between the pattern of the decoration sheet and the concave or convex contour of the molded body, thus failing to achieve desired foil decoration on the surface of molded body. In an extreme case, wrinkling or breakage may occur.
The problems caused by the stretching of the decoration sheet can be avoided to some extent by preliminarily heating to soften the decoration sheet by the hot platen as described above; but, even in that case, if a molded body had large level differences or curvature of surface, wrinkles or distortion would tend to appear because of increase of the stretching and drawing amounts of the decoration sheet. Therefore, it was difficult to effect foil decoration as expected. Further, if the stretching speed is decreased to relief the stress in order to deform the heated and softened decoration sheet in large stretching and drawing amounts, strain deformation of the sheet becomes distinct in this case because of its own weight or the like during a period before it reaches the cavity surface.